1. Field of the Invention
This invention concerns improved heat curable, adhesive compositions of the type commonly used in manufacturing for adhesive, gap-filling and sealing purposes in joining components, including automotive applications.
2. Description of the Prior Art
In manufacturing vehicle bodies, joints between component parts may be secured, filled or sealed with adhesive compositions which are then cured to develop full strength and durability of the joints and seals by passing the assembled body through a stoving oven. Preferred adhesive compositions are described in U.S. Pat. No. 4,600,745 as including
liquid polybutadiene polymer, PA0 powdered sulfur, PA0 organic accelerator, PA0 inert fillers.
The liquid polybutadiene polymer in such formulations contains most of the unsaturation in the cis 1,4 configuration. Such adhesive compositions are pastes at normal room temperature and may be cured by heating. The cured compositions show good adhesion to degreased steel, mild steel coated with mill oil and mild steel coated with anodic or cathodic electrophoretic primers.
These prior art compositions have not exhibited adequate adhesion to zinc coated steel, e.g., electro deposition zinc coatings or hot-dip galvanized coatings. The prior art compositions also have a tendency to "popping" when the adhesively joined metal components are subsequently spot-welded at high temperatures. "Popping" is a phenomenon associated with thermal deterioration of the adhesive which is manifested by audible "pops".